For processes for industrially preparing a polyolefin from an olefin, the liquid polymerization process, the slurry polymerization process, and the gas phase polymerization process, have been known. Since in the liquid polymerization process a polymer is dissolved in a liquid phase and the polymerization is conducted in a homogeneous phase, this process has a defect in that much energy is needed to separate the polymer from a solvent and the device for the polymerization becomes complicated.
In contrast, in the slurry polymerization process and the gas phase polymerization process since the polymerization is conducted in a liquid phase and a gas phase, respectively, to obtain a solid particulate polymer, they have such advantages that the separation of the polymer is easy and the device for the polymerization can be simplified. However, although in those polymerization processes it is necessary that solid particles do not adhere to one another, in the process for preparing a rubbery polymer having adhesive properties adhesion occurs between the particles or between the particles and the surface of the wall of the reactor or the transport line, and thus the particles accumulate, and cause a phenomenon that makes preparing the polymer impossible (fouling).
Accordingly, conventionally, the slurry polymerization process and the gas-phase polymerization process have been adopted for the preparation of a polymer that has crystalline properties and has little adhesion properties, but have not been adopted for the industrial preparation of an ethylene-based copolymer such as an ethylene-.alpha.-olefin copolymer and an ethylene-.alpha.-olefin-unconjugated diene terpolymer, which is required to have rubbery properties and which is obtained by a polymerization especially using at least one kind of transition metal-based catalyst selected from the group consisting of V, Zr, and Hf, because intensive fouling occurs when a continuous operation is conducted for a long time. For the industrial preparation of the rubbery copolymers, the liquid polymerization process or a slurry polymerization process that is done by adding a large quantity of a solvent and is thus substantially similar to the liquid polymerization process, has been adopted.
To prevent the adhesion of the polymer particles, a process has been proposed in which an antistatic agent, etc., is added in the polymerization reactor when ethylene and an .alpha.-olefin are polymerized in the presence of a V, Zr, and Hf-based catalyst to obtain a rubbery copolymer (Japanese Patent Early-publication No. 56-51164, Japanese Patent Early-publication No. 59-64604, Japanese Patent Early-publication No. 61-7307, and Japanese Patent Early-publication No. 61-57608). Those processes are proved to have effects in preparing a polymer having strong crystalline properties or when a batch-wise polymerization is done in a small autoclave; however, they are insufficient in preventing fouling in the industrial preparation of a rubbery copolymer with a V, Zr, and Hf-based catalyst by a continuous operation over a long period.
Japanese Patent early-publication 60-94412 proposes that when a slurry polymerization is conducted in the presence of a Ti-based catalyst the coating film layer of a polysiloxane compound is formed in advance on the surface of the inner wall of a reactor or the part which a reacting catalyst contacts, and this prevents adhesion of the produced rubbery polymer to the surface of the wall, etc. However, a slurry polymerization using at least one kind of transition metal-based catalyst, said transition metal being selected from the group consisting of V, Zr, and Hf, cannot be industrially adopted, since in comparison with a slurry polymerization using a Ti-based catalyst, the produced polymer is a more random and rubbery copolymer, intensive fouling occurs, and the adhesion among particles cannot be prevented even if the above-mentioned countermeasure is taken. The above processes have such defects wherein forming a coating film layer of a polysiloxane on the inner wall of a reactor or on the part of the surface which a reaction medium contacts is needed, and thus the cost of the preparation becomes higher.